The present invention relates to a metal laminate gasket with a stepped sealing portion on a metal plate for securely sealing around a hole.
A metal gasket or metal laminate gasket has been used widely since the metal gasket is strong against high temperature and pressure.
In one type of a metal laminate gasket formed of three or more metal plates, one metal plate with a curved portion and another metal plate with an inner portion are assembled together to prevent fluid from entering between the plates, such as U.S. Pat. No. 4,728,110 and No. 4,776,601. FIG. 4 shows this kind of a gasket.
As shown in FIG. 4, the gasket G is formed of an upper plate 10 with an inner portion 10a, a middle or surface pressure regulating plate 11, a middle plate 12 with a bead 12a, and a lower plate 13 with a curved portion 13a and a flange 13b. A space S is formed laterally between the flange 13b and the middle plate 11. When the gasket G is tightened, apart of the upper plate 10 can be bent easily so that the inner portion 10a is located under the flange 13b.
When the gasket G is situated between a cylinder head and a cylinder block (both not shown) and is tightened, the gasket G provides a surface pressure P by the bead 12a near a cylinder bore Hc, i.e. main sealing portion, and a surface pressure p away from the cylinder bore. The surface pressure p is less than the surface pressure P.
In the space S, a number of the plates for constituting the gasket is reduced, and a part of the upper plate 10 is inclined to be located under the flange 13b. Therefore, when the gasket G is tightened, a surface pressure is not formed on the space S.
In this situation, if there is a deficiency in one part of the main sealing portion around the cylinder bore Hc, a fluid leaks from that part and flows along the space S. If the surface pressure p is not even throughout the entire area, the fluid in the space S flows into a lower surface pressure portion and spreads over the gasket.
The present invention has been made in view of the above situation, and an object of the invention is to provide a metal laminate gasket, which can provide a surface pressure continuously at a main sealing portion and a vicinity thereof to securely seal around a hole to be sealed.
Another object of the invention is to provide a metal laminate gasket as stated above, which can provide a surface pressure outside the main sealing portion evenly without forming a non-surface pressure area.
A further object of the invention is to provide a metal laminate gasket as stated above, which can be easily and economically formed.
Further objects and advantages of the invention will be apparent from the following description of the invention.